The present invention relates generally to rotary driven cutters and scarifiers for use in earth working, mining, and other in situ disintegration of hard materials. The invention is particularly directed to cutting bit holders which are fixed to a surface portion of a rotary driven member such as a cylindrical drum and has particular utility in connection with roadway planing machines, also known as roadway surface reclaiming machines, which are employed prior to roadway resurfacing.
Typical roadway surface reclaiming machines disclosed in the prior art include rotary driven cylindrical drums to which are fixed holders holding one or more cutting bits which scarify and mine the top portion of an asphaltic road surface. While several styles of drums have been employed, at least some styles have included an array of cutting bit holders fixed usually by a peripheral weld to the drum surface. Replaceable cutting bits are received within the cutting bit holders which can be periodically replaced as needed depending upon the amount of wear suffered as a result of the road surface mining operation. Examples of prior art cutting bit holders are to be found in U.S. Pat. Nos. 5,582,468 and 5,098,167, as well as the prior art cited therein.
During the operation of such roadway surface reclaiming machines, a cutting bit and/or a cutting bit holder may strike a particularly hard portion of the road surface in such a way to cause significant damage to the cutting bit holder. The shearing forces in such a situation can be sufficient to shear part or all of one or more of the cutting bit holders from the surface of the rotary driven drum or other driven member thus mandating an immediate replacement of the lost or damaged holders in the field by welding new cutting bit holders to the drum surface. Such a replacement requires that the surface of the drum be prepared to receive the replacement cutting bit holder and can include using a cutting torch to remove any remaining portion of a cutting bit holder as well as a hand held grinder to grind away any residual portion of the weld which held the damaged cutting bit holder to the surface.
Such drum surface preparation is rarely completely satisfactory and generally leaves a roughened surface to which the new cutting bit holder is to be applied. The roughness of the drum surface often prevents the correct alignment of the new cutting bit holder and as a result further damage to the replacement cutting bit holder or other holders adjacent to or aligned with the replaced cutting bit holder are increasing susceptible to accelerated wear and potential damage. Even small changes in alignment of a cutting bit holder of a few degrees can also contribute to substantially accelerated wear of the cutting bits which are removably inserted into the cutting bit holders.
Thus, an object of the present invention is to provide a cutting bit holder and a drum surface adapted to receive a cutting bit holder which is designed to preserve a reference surface engaged by the cutting bit holder, but protected from alteration during replacement of the cutting bit holder, to assure proper alignment of the replacement structure. An additional objection of the present invention is to provide a cutting bit holding element which is designed for field replacement, yet will maintain the originally designed alignment of the cutting bit with respect to the drum assembly as a whole.